Diabetes mellitus is a disorder in which the pancreas cannot create sufficient insulin (Type I or insulin dependent) and/or in which insulin is not effective (Type 2 or non-insulin dependent). In the diabetic state, the victim suffers from high blood sugar, which can cause an array of physiological derangements associated with the deterioration of small blood vessels, for example, kidney failure, skin ulcers, or bleeding into the vitreous of the eye. A hypoglycemic reaction (low blood sugar) can be induced by an inadvertent overdose of insulin, or after a normal dose of insulin or glucose-lowering agent accompanied by extraordinary exercise or insufficient food intake.
Conventionally, a person with diabetes carries a self-monitoring blood glucose (SMBG) monitor, which typically requires uncomfortable finger pricking methods. Due to the lack of comfort and convenience, a person with diabetes normally only measures his or her glucose levels two to four times per day. Unfortunately, such time intervals are so far spread apart that the person with diabetes likely finds out too late of a hyperglycemic or hypoglycemic condition, sometimes incurring dangerous side effects. Glucose levels may be alternatively monitored continuously by a sensor system including an on-skin sensor assembly. The sensor system may have a wireless transmitter that transmits measurement data to a receiver that processes and displays information based on the measurements. Such sensor systems are sometimes referred to as continuous glucose monitors (CGMs).
Continuous glucose sensors are typically transported by the use of various sterile package systems. One common method for packaging implantable sensors involves “bagging” the device in a flexible bag. Because the glucose sensors are not secured in fixed positions, these sensors will often shift and tumble within the package when the package is moved. Because of susceptibility to movement of sensors within the package and because of uneven distribution of radiation emitted to different positions within the package, sterilization of glucose sensors typically requires that the package is subjected to a substantially higher dosage of radiation than what would be required if the glucose sensors were secured to fixed positions within the package. Accordingly, in many instances, the dosage emitted is at a setting such that the different locations of within the package may receive a radiation dosage from about 25 kGray to about 35 kGray.
Not only is this a wide range of radiation dosage, but the high overall dosage is required to ensure that the sterilization meets the required standards to account for the possibility that the glucose sensors may shift to locations within the package that receive a lower dosage of radiation than other locations that receive a higher dosage of radiation. Consequently, for various reasons, a glucose sensor that receives a higher dosage of radiation (e.g., 35 kGray) may have a shortened sensor lifetime, as compared to a glucose sensor that receives a lower dosage of radiation (e.g., 25 kGray). For example, a higher dosage of radiation can denature a percentage of the glucose sensor's enzymes used to break down glucose to produce a measured species indicative of glucose concentration. Additionally, a higher overall dosage of radiation may also damage the adhesiveness of the adhesive patch used to adhere an ex vivo portion of a glucose sensor system to the skin. Furthermore, another drawback to the use of a higher overall dosage of radiation is that potential damage to the package—for example, damage to ink printed on the package/container to provide graphics and damage to certain contents (e.g., an instruction manual) received by the package—becomes more pervasive at high radiation dosages. Heretofore, a separate package/container was used to hold the glucose sensor during the sterilization process. Afterwards, the glucose sensor was taken out of the sterilization package and then placed into a final package which is then shipped out for use.
Conventionally, the radiation dosage range often used is from about 25 kGray to about 35 kGray for implantable glucose sensors. With the product advantage of having the products secured in a fixed position and fixed orientation, such that each product receives substantially an equal dosage of the radiation, the higher end of the setting range can be lowered to reduce the risk of enzyme denaturing. For example, in one embodiment, the radiation dosage range applied may be from about 25 kGray to about 30 kGray. In still another embodiment, lower radiation setting of the range may be about 10 kGray, 15 kGray, 20 kGray, or 25 kGray, and the upper radiation setting of the range may be about 25 kGray, 30 kGray, or 35 kGray.
When a package contains a plurality of glucose sensors, and these sensors are shifted to different positions and/or orientations within a package prior to or during sterilization, the sensors may each receive different amounts of radiation and a different radiation profile. This difference in radiation dosage may result in inconsistent sensor properties and thus inconsistent sensor performance among sensors. Accordingly, it is desirable to package the glucose sensors in a manner that prevents or substantially minimizes sensor movement within the package. It is also desirable to sterilize the glucose sensors in a manner that permits substantial consistency in radiation dosage received and substantial consistency in radiation profile.